Canola oil has the lowest level of saturated fatty acids of all vegetable oils. As consumers become more aware of the health impact of lipid nutrition, consumption of canola oil in the U.S. has increased. However, canola oil extracted from many natural and commercial varieties of rapeseed contains a relatively high .alpha.-linolenic acid content (C.sub.18:3 ; all cis 9,12,15 octadecatrienoic acid; ALA). The oil is unstable and easily oxidized during cooking, which in turn creates off-flavors and compromises the sensory characteristics of foods cooked in such oils. It also develops unacceptable off odors and rancid flavors during storage.
Hydrogenation can be used to improve performance attributes by lowering the amount of linoleic and .alpha.-linolenic acids in the oil. Hydrogenation converts cis mono- and cis poly-unsaturated fatty acids into trans-fatty acids and saturated fatty acids. Saturated and trans-fatty acids are not desirable for health reasons. It would be desirable to reduce the level of polyunsaturates in order to improve the oxidative stability and the shelf life of these oils while minimizing the increase in trans-fatty acids and saturated fatty acids.
Different vegetable oils can be blended to reduce the .alpha.-linolenic acid content and improve performance attributes. However, blending canola oil with other vegetable oils such as cottonseed oil increases the saturated fatty acid content of the final product and decreases the healthy attributes of canola oil.
.alpha.-Linolenic acid has been reported to have a relatively low oxidative stability. In general, the oxidative stability of oleic acid is about 10 fold greater than that of linoleic acid, and the oxidative stability of linoleic acid is about 2 fold greater than that of linolenic acid.
Linoleic and .alpha.-linolenic acids have been suggested as precursors to undesirable odor and flavor development in foods. To improve the functionality of canola oil, the University of Manitoba developed the canola variety "Stellar" which has reduced .alpha.-linolenic acid (Scarth et al., Can. J. Plant Sci., 68:509-511 (1988)). The low .alpha.-linolenic acid oil was reduced in odor when heated in air, but still remained unacceptable to the sensory panel in flavor evaluations (Eskin et al., J. Am. Oil Chem. Soc. 66:1081-1084 (1989)). The oxidative stability of Stellar oil increased by 17.5% over the commercial variety Westar as measured by Active Oxygen Method (AOM) hours. (Can. J. Plant Sci. (1988) Vol. 68, pp. 509-511).
European Patent Application, EP 0 323 753 A1 describes a canola oil having an enhanced oleic acid content and suggests that such an oil would have increased heat stability in combination with other traits. The application describes a canola oil with reduced .alpha.-linolenic acid. However, no flavor or performance testing was reported for any oil.
The factors affecting oxidative stability and flavor stability of canola oils are not completely understood, although it is known that the amount of .alpha.-linolenic acid in the oil affects oxidative stability and flavor stability. A canola oil is needed that possesses very high oxidative stability and improved flavor and odor characteristics.